1. Field of the Invention
This invention relates to techniques for conditioning gaseous samples and for controlling the environment in which such samples are analyzed.
2. General Background
Analysis of a subject's exhaled breath is a promising clinical tool, with potential application in the diagnosis and management of many conditions. For instance, changes in nitric oxide (NO) concentration in exhaled breath can indicate a change in the level of inflammation in the airway of an asthmatic, indicating an increase in the likelihood of an asthma attack. Excessive carbon monoxide (CO) can indicate hemolytic jaundice, and high levels of hydrogen can indicate carbohydrate malabsorption.
To quantify the concentration of gases, various sensors have been developed. Some of these sensors detect and measure changes in bioactive substances in response to a gaseous analyte. For instance, a sensor developed by the present inventors measures the optically-quantifiable changes in a sensing element comprised of sol-gel encapsulated cytochrome-c in response to NO. This sensor and related technology are disclosed in the following U.S. patent applications, the disclosures of which are hereby incorporated herein by reference: Ser. No. 10/334,625, filed 30 Dec. 2003, Ser. No. 10/767,709, filed 28 Jan. 2004, and U.S. Provisional Application No. 60/398,216 filed Jul. 23, 2002.
It is difficult to build an exhaled breath analyzer because of the interfering effects of humidity and other constituents of the ambient atmosphere and of the exhaled breath. Also, temperature variations can compromise sensor accuracy. These difficulties are especially acute when the device is designed to measure trace gases, such as NO, since the exquisite sensitivity required for such analyzers also makes the devices much more sensitive to changes in the testing conditions. Thus, any device that seeks to quantify trace analytes in exhaled breath must somehow minimize or account for these variables.
In particular, in building their NO sensor, the applicants have learned that (i) the relative humidity around the sensing element must be controlled during storage to preserve the sensor's reactivity and sensitivity, (ii) the relative humidity of the gas stream (exhaled breath) must be controlled with the relative humidity of the sensor, (iii) the sensor should be stored in an environment substantially free of the analyte of interest, such as NO, (iv) the incoming stream of exhaled breath may need to be scrubbed or purged of interfering breath components, such as carbon dioxide, and (v) the sensor is susceptible to temperature variations, and therefore the temperature of the sensor must be set and controlled at a predetermined level.
By conditioning and controlling the exhaled breath sample and the sensor's environment, a workable, commercially-viable trace gas exhaled breath sensor can be manufactured.